.\" Copyright 1993 Rickard E. Faith (faith@cs.unc.edu)
.\" May be distributed under the GNU General Public License
.TH LOGIN "1" "June 2012" "util-linux" "User Commands"
.SH NAME
login \- begin session on the system
.SH SYNOPSIS
.B login
[
.B \-p
] [
.B \-h
.I host
] [
.B \-H
] [
.B \-f
.I username
|
.I username
]
.SH DESCRIPTION
.B login
is used when signing onto a system.  If no argument is given,
.B login
prompts for the username.
.PP
The user is then prompted for a password, where appropriate.  Echoing
is disabled to prevent revealing the password.  Only a small number
of password failures are permitted before
.B login
exits and the communications link is severed.
.PP
If password aging has been enabled for the account, the user may be
prompted for a new password before proceeding.  They will be forced to
provide their old password and the new password before continuing.
Please refer to
.BR passwd (1)
for more information.
.PP
The user and group ID will be set according to their values in the
.I /etc/passwd
file.  There is one exception if the user ID is zero: in this case,
only the primary group ID of the account is set.  This should allow
the system administrator to login even in case of network problems.
The value for
.BR $HOME ,
.BR $USER ,
.BR $SHELL ,
.BR $PATH ,
.BR $LOGNAME ,
and
.B $MAIL
are set according to the appropriate fields in the password entry.
.B $PATH
defaults to
.I /usr\:/local\:/bin:\:/bin:\:/usr\:/bin
for normal users, and to
.I /usr\:/local\:/sbin:\:/usr\:/local\:/bin:\:/sbin:\:/bin:\:/usr\:/sbin:\:/usr\:/bin
for root, if not otherwise configured.
.P
The environment variable
.B $TERM
will be preserved, if it exists (other environment variables are
preserved if the
.B \-p
option is given), else it will be initialized to the terminal type on your tty.
.PP
Then the user's shell is started.  If no shell is specified for the
user in
.IR /etc\:/passwd ,
then
.I /bin\:/sh
is used.  If there is no directory specified in
.IR /etc\:/passwd ,
then
.I /
is used (the home directory is checked for the
.I .hushlogin
file described below).
.PP
If the file
.I .hushlogin
exists, then a "quiet" login is performed (this disables the checking
of mail and the printing of the last login time and message of the
day).  Otherwise, if
.I /var\:/log\:/lastlog
exists, the last login time is printed (and the current login is
recorded).
.SH OPTIONS
.TP
.B \-p
Used by
.BR getty (8)
to tell
.B login
not to destroy the environment.
.TP
.B \-f
Used to skip a login authentication.  This option is usually
used by the
.BR getty (8)
autologin feature.
.TP
.B \-h
Used by other servers (i.e.,
.BR telnetd (8))
to pass the name of the remote host to
.B login
so that it may be placed in utmp and wtmp.  Only the superuser may
use this option.
.IP
Note that the
.B \-h
option has an impact on the
.B PAM service
.BR name .
The standard service name is
.IR login ,
but with the
.B \-h
option, the name is
.IR remote .
It is necessary to create proper PAM config files (e.g.,
.I /etc\:/pam.d\:/login
and
.IR /etc\:/pam.d\:/remote ).
.TP
.B \-H
Used by other servers (i.e.,
.BR telnetd (8))
to tell
.B login
that printing the hostname should be suppressed in the login: prompt.
See also
.B LOGIN_PLAIN_PROMPT
below if your server does not allow the
.B login
command line to be configured.
.TP
\fB\-\-help\fR
Display help text and exit.
.TP
\fB\-V\fR, \fB\-\-version\fR
Display version information and exit.
.SH CONFIG FILE ITEMS
.B login
reads the
.IR /etc\:/login.defs (5)
configuration file.  Note that the configuration file could be
distributed with another package (e.g., shadow-utils).  The following
configuration items are relevant for
.BR login :
.PP
.B MOTD_FILE
(string)
.RS 4
Specifies a ":" delimited list of "message of the day" files and directories
to be displayed upon login.  If the specified path is a directory then displays
all files with .motd file extension in version-sort order from the directory.
.PP
The default value is
.IR "/usr/share/misc/motd:/run/motd:/etc/motd" .
If the
.B MOTD_FILE
item is empty or a quiet login is enabled, then the message of the day
is not displayed.  Note that the same functionality is also provided
by the
.BR pam_motd (8)
PAM module.
.PP
The directories in the
.B MOTD_FILE
are supported since version 2.36.
.PP
Note that
.B login
does not implement any filenames overriding behavior like pam_motd
(see also
.BR MOTD_FIRSTONLY ),
but all content from all files is displayed.  It is
recommended to keep extra logic in content generators and use
.I /run/motd.d
rather
than rely on overriding behavior hardcoded in system tools.
.RE
.PP
.B MOTD_FIRSTONLY
(boolean)
.RS 4
Forces
.B login
to stop display content specified by
.B MOTD_FILE
after the first accessible item in the list.
Note that a directory is one item in this case.
This option allows
.B login
semantics to be configured to be more compatible with pam_motd.
.RE
.PP
.B LOGIN_PLAIN_PROMPT
(boolean)
.RS 4
Tell
.B login
that printing the hostname should be suppressed in the login:
prompt.
This is an alternative to the \fB\-H\fR command line option.  The default
value is
.IR no .
.RE
.PP
.B LOGIN_TIMEOUT
(number)
.RS 4
Maximum time in seconds for login.  The default value is
.IR 60 .
.RE
.PP
.B LOGIN_RETRIES
(number)
.RS 4
Maximum number of login retries in case of a bad password.  The default
value is
.IR 3 .
.RE
.PP
.B LOGIN_KEEP_USERNAME
(boolean)
.RS 4
Tell
.B login
to only re-prompt for the password if authentication failed, but the username is valid. The default value is
.IR no .
.RE
.PP
.B FAIL_DELAY
(number)
.RS 4
Delay in seconds before being allowed another three tries after a
login failure.  The default value is
.IR 5 .
.RE
.PP
.B TTYPERM
(string)
.RS 4
The terminal permissions.  The default value is
.I 0600
or
.I 0620
if tty group is used.
.RE
.PP
.B TTYGROUP
(string)
.RS 4
The login tty will be owned by the
.BR TTYGROUP .
The default value is
.IR tty .
If the
.B TTYGROUP
does not exist, then the ownership of the terminal is set to the
user\'s primary group.
.PP
The
.B TTYGROUP
can be either the name of a group or a numeric group identifier.
.RE
.PP
.B HUSHLOGIN_FILE
(string)
.RS 4
If defined, this file can inhibit all the usual chatter during the
login sequence.  If a full pathname (e.g.,
.IR /etc\:/hushlogins )
is specified, then hushed mode will be enabled if the user\'s name or
shell are found in the file.  If this global hush login file is empty
then the hushed mode will be enabled for all users.
.PP
If a full pathname is not specified, then hushed mode will be enabled
if the file exists in the user\'s home directory.
.PP
The default is to check
.I /etc\:/hushlogins
and if it does not exist then
.I ~/.hushlogin
.PP
If the
.B HUSHLOGIN_FILE
item is empty, then all the checks are disabled.
.RE
.PP
.B DEFAULT_HOME
(boolean)
.RS 4
Indicate if login is allowed if we cannot change directory to the
home directory.  If set to
.IR yes ,
the user will login in the root (/) directory if it is not possible
to change directory to their home.  The default value is
.IR yes .
.RE
.PP
.B LASTLOG_UID_MAX
(unsigned number)
.RS 4
Highest user ID number for which the
.I lastlog
entries should be
updated.  As higher user IDs are usually tracked by remote user
identity and authentication services there is no need to create
a huge sparse
.I lastlog
file for them.  No LASTLOG_UID_MAX option
present in the configuration means that there is no user ID limit
for writing
.I lastlog
entries.
.RE
.PP
.B LOG_UNKFAIL_ENAB
(boolean)
.RS 4
Enable display of unknown usernames when login failures are recorded.
The default value is
.IR no .
.PP
Note that logging unknown usernames may be a security issue if a
user enters their password instead of their login name.
.RE
.PP
.B ENV_PATH
(string)
.RS 4
If set, it will be used to define the
.B PATH
environment variable when
a regular user logs in.  The default value is
.I /usr\:/local\:/bin:\:/bin:\:/usr\:/bin
.RE
.PP
.B ENV_ROOTPATH
(string)
.br
.B ENV_SUPATH
(string)
.RS 4
If set, it will be used to define the PATH environment variable when
the superuser logs in.  ENV_ROOTPATH takes precedence.  The default value is
.I /usr\:/local\:/sbin:\:/usr\:/local\:/bin:\:/sbin:\:/bin:\:/usr\:/sbin:\:/usr\:/bin
.RE
.SH FILES
.nf
.I /var/run/utmp
.I /var/log/wtmp
.I /var/log/lastlog
.I /var/spool/mail/*
.I /etc/motd
.I /etc/passwd
.I /etc/nologin
.I /etc/pam.d/login
.I /etc/pam.d/remote
.I /etc/hushlogins
.I .hushlogin
.fi
.SH BUGS
The undocumented BSD
.B \-r
option is not supported.  This may be required by some
.BR rlogind (8)
programs.
.PP
A recursive login, as used to be possible in the good old days, no
longer works; for most purposes
.BR su (1)
is a satisfactory substitute.  Indeed, for security reasons,
.B login
does a
.BR vhangup (2)
system call to remove any possible listening
processes on the tty.  This is to avoid password sniffing.  If one
uses the command
.BR login ,
then the surrounding shell gets killed by
.BR vhangup (2)
because it's no
longer the true owner of the tty.  This can be avoided by using
.B exec login
in a top-level shell or xterm.
.SH AUTHORS
Derived from BSD login 5.40 (5/9/89) by
.MT glad@\:daimi.\:dk
Michael Glad
.ME
for HP-UX
.br
Ported to Linux 0.12:
.MT poe@\:daimi.\:aau.\:dk
Peter Orbaek
.ME
.br
Rewritten to a PAM-only version by
.MT kzak@\:redhat.\:com
Karel Zak
.ME
.SH SEE ALSO
.BR mail (1),
.BR passwd (1),
.BR passwd (5),
.BR utmp (5),
.BR environ (7),
.BR getty (8),
.BR init (8),
.BR lastlog (8)
.BR shutdown (8)
.SH AVAILABILITY
The login command is part of the util-linux package and is
available from
.UR https://\:www.kernel.org\:/pub\:/linux\:/utils\:/util-linux/
Linux Kernel Archive
.UE .
